Oh, and the clots you see could just be clumps of tissue from your uterine lining.
I have clots every time I'm on my period, I think it's normal for some women. I doubt it's why you haven't gotten pregnant, I have a son, and therefore have gotten pregnant with having clots during my period. If you are having very large clots I would recommend seeing a gynecologist, but if they're small I wouldn't worry too much.